Electrical apparatus



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ATTORNEYS Patented Jan. 13,A 1,953

ELECTRICAL APPARATUS Arthur W. Hayden, Cheshire, Conn., assigner toPhilips Laboratories, Inc., Irvington-on-Hudson, N. Y., a corporation ofDelaware Application May 23, 1950, Serial No. 163,649

Claims. (Cl. 307-41) 1 This invention relates to electrical switchingapparatus for successively supplying current from a common source to aplurality of electric circuits. It is more particularly concerned with,and therefore Will be ydescribed in connection with, such an Y apparatusfor successively causing the energization of the propeller de-icingcircuits of an airplane.

For de-icing the blades of airplane propellers, it has been establishedthat it is much more satisfactory to supply current to heating elementsbuilt into the leading edge of the propeller blades at regular intervalsfor relatively short periods of time, rather than to supply continuouscurrent thereto. In addition it has been found that ice does notaccumulate near the tips of the blades, possibly due to highercentrifugal forces and air velocity. It has also been found that due tothe characteristics of the air stream passing over the propeller blades,ice is ydeposited only on the leading edges of the blades. Thus, iceactually accumulates only on about two-thirds of the leading edge ofeach of the blades, By allowing it to accumulate there, it is onlynecessary to heat the propeller blade along two-thirds of its leadingedge, until the adhesion of the undersurface of the ice coating isbroken, in order to throw it off by the centrifugal force produced byrotation of the blades. This avoids the necessity of heating the entireblade, or of melting all of the accumulated ice, or of keeping all theblades continuously above the freezing point. The ice acts as aninsulating blanket reducing the heat loss as the blade rotates in thecold atmosphere, and thus reduces the amount of current required tobring the blade up above the melting point of the ice. Continuousheating of the leading edge of the blade would cause the ice to melt andrun back on the trailing edge, where it would freeze unless the entireblade were heated.

In airplanes having multiple engines, a further advantage is gained inthat the on time of the various heaters may be arranged in small groupsin consecutive non-overlapping relation, whereby only two or threeblades of the airplanes propellers are de-iced at one time. In orderthat a state of unbalance will not exist as de-icing takes place, twoopposing blades of a four-bladed propeller are de-iced simultaneously.In the case of an airplane provided with three-bladed prO- pellers, itwill be clear, of course, that in order to avoid unbalance and theresultant detrimental vibration caused thereby the heaters in all threeblades must be energized at the same time.

It will readily be appreciated that a considerable reduction in currentrequirements is thereby effected, resulting in an appreciable saving insize, weight, and cost of the necessary current generating equipment anda corresponding increase in the airplanes load carrying capacity. Theimportance of this will be easily appreciated when it is realized thatlarger generators mean larger engines to drive the combined load opropeller and generator and more gasoline to supply the addedhorsepower. Pay load is thus reduced by increased weight of generator,engine, and gasoline all combined.

It is among the primary objects of this invention to provide apparatusby which the heating elements in the propellers of an airplane may besupplied with current in succession and at regular intervals. Theapparatus must be simple, reliable and remain in accurately timedcondition indenitely so that there will be negligible pause and nooverlap between the breaking of the current flow to one heating elementcircuit and the initiation of current flow to the next successivecircuit.

Another object of this invention is to provide an apparatus for theabove described purpose which constitutes an improvement over theapparatus disclosed in the R. G. Hoof, U. S. Patent 2,466,238. Theapparatus disclosed in that patent employs a combination of commutatortype switches and a cam actuated switch, the commutator type switchessuccessively preparing paths to the different heating element controlcircuits in overlapping relation and the circuits being completed by camactuation of a double throw switch which simultaneously breaks one ofthe paths created by the commutator switches and completes another path.When the cam actuated double throw switch is next actuated thecommutator type switches have prepared a new circuit to be completedthereby. In Hoofs apparatus the double throw switch is actuated onceeach time one circuit is broken and a new one completed. Therefore, inan apparatus adapted to handle the making and breaking of, for instance,eight circuits the double throw switch will of necessity be actuatedeight times per cycle.

The apparatus of the present invention is designed to be relatively muchsimpler and less costly than that disclosed in the Hoof patent and toeliminate the necessity of closing any single switch every time thecommon source of current is connected to a different heating elementcontrol circuit. Hence, the lives of the switches involved areconsiderably increased and replacevelectric circuits.

ment thereof and the costs incident thereto are less frequentlynecessary.

According to this invention, apparatus for successively supplyingcurrent from a common source to a plurality of electric circuitscomprises rst and second double throw switches the switch contacts ofwhich are electrically connected, respectively, to one each of theterminals of the A third double throw switch is provided and has itsswitch contacts electrically connected, respectively, to the switch armsof the first and second double throw switches. The switch arm of thethird double throw switch is adapted to be electrically .connected tothe common source. The apparatus also includes a constant speed electricmotor and means for mechanically connecting the motor to the switches tocause the switches to be operated in sequence when the motor is operatedand to cause each switch to perform at least one electrical transferduring a complete cycle of operation of the apparatus. Each electriccircuit is thereby successively supplied with current from the commonsource during the cycle of operation.

It is contemplated, though the invention should not necessarily besovlimited, that the means for mechanically connecting the motor to thedouble throw switches be either a cam shaft driven by the electric-motorand having xedly secured to it a single cam adapted to operate insequence all of the switches, or a cam shaft driven by the electricmotor having aplurality of substantially identical cams (one for eachswitch) fixedly secured thereto and so positioned circumferentially withrespectto one another that each of the switches is operated in sequence.

For a more detailed description'of several speciiic forms of theapparatus of this invention, reference may be made to the accompanyingdrawings in which:

Fig. 1 is a schematic diagram of one form of the apparatus which may beused in the distribution of heating current to four 4bladed propellers;

Fig. 2 is a perspective View showing the arrangement of the cams, doublethrow switches and cam shaft;

Fig. 3 is a schematic diagram ofa modified form of apparatus for use inthe distribution of heating current to four 3-bladed propellers; and

Fig. 4 is a schematic diagram of another modified form of apparatus foruse in the distribution of heating current to four 3-bladed propellers.

In Fig. 1 there are shown four 4-b1aded propellers It, II, I2 and I3,each being of the same design. In each blade I4 of eachpropeller thereis mounted a heating element I5. As pointed out previously, reduction incost of the airplanes generating equipment and increase in theairplanesload carrying capacity may be accomplished and more effective de-icingobtained by arranging the heater circuits so that a minimum number ofheaters are connected at the same instant, care being taken not to causemechanical unbalance as the blades are de-iced. In order that anunbalance does not result in any of the four-bladed propellers, twoelements are supplied with current simultaneously, each in an oppositeblade of one propeller. Thus, in each propeller the heating elements I5in a pair of opposite blades I4 are connected together in one heatingelement circuit. Hence, in a four-i-bladed propeller airplane there areeight heating circuits that must be energized in sequence, withnegligible pause and no overlap for greatest eirlciency.

The means by which current is provided to the heating elements of onepropeller is identical to the means provided for supplying current tothe heating elements of another, and therefore a description of thismeans for one propeller will suince to describe the means for all of thepropellers. In propeller It the two heating circuits may be designatedas IE5 and I6'. One terminal of each of the heating circuits isconnected by conductor I7 to a slip ring I8 mounted on a shaft ifirotating with the propeller. A brush 2li is provided to ground slip ringI8 at all times and thus it will be understood that one terminal of eachof the heating circuits I6 and I5 is always grounded. Current may beprovided to heating circuit I5 through a conductor 2! connected to theungrounded terminal of this heating circuit and to a slip ring 22 alsomounted on shaft I. A brush 23 is provided to supply current to the slipring 22. The ungrounded terminal of heating circuit I6 is connected by aconductor 24 to a slip ring 25 also mounted on shaft I9, and adapted tobe provided with current through brush 26. Brushes 23 and E6 areconnected, respectively, by conductors 2l and 28 to switch contacts 2sof a pair of relays St.

`Armatures 3i of the relays are normally maintained by springs 32 out ofcontact with relay contacts 29. These armatures are connected throughconductors 33 to a common source of current capable of supplying thedesirable heavy current to one heating circuit (composed of two heatingelements).

Each of the relays has one terminal grounded at 313. The other terminalsof the eight relays 3S are connected, respectively, by conductors 3B,3l, 3S, 39, lit, 11,152 and d3 to terminals 45, 45, lil, 48, 139, 5G, 5land 52 of a terminal board 53.

My apparatus is designed to successively supply current to the terminalsS- so that the eight relays 3Q may be successively energized to closetheir relay switches 2S and thereby successively provide a heavy currentrom the common source tothe heating element circuits.

By reference to Figs. l and 2, my apparatus may be seen to comprise aconstant speed electric motor. Ell which Vdrives a cam shaft d5 throughsuitable reduction gearing 55 (Fig. 2). Cams A, B, C, D, E, F, .and Gare ixedly mounted on cam shaft 55 and are adapted to be rotated therebyto operate, respectively, double throw switches A', B', C', D', E', andG. These cams are identical to one another and have dwells ofapproximately degrees. Cain followers 55, through which the cams operatetheir respective double throw switches, may be best seen in Fig. 2although they are shown schematically in Fig. 1. Each of the doublethrow switches comprises,

as the name implies, a switch arm and two switch contacts 58 and 59(Fig. l). Normally the switch arm is maintained in contact with switchcontact 5S, as by spring means (not shown), and must be positively urgedby its associated cam into contact with switch Contact 555.

The switch contacts of double throw switches D', E', F and G (eight innumber) are respectively connected to terminals i5-52 of the terminalboard E3. For instance, in the case of double throw switch D', itsswitch contact 5a is electrically connected to terminal i5 of theterminal board and its switch contact 58 is electrically connected toterminal 4t of the terminal board. The switch contacts of double throwswitches B', and C' (four in number) are electrically connected,respectively, to the switch arms 51 of double throw switches D'-G. Forinstance, in the case of double throw switch B', its switch contact 59is electrically connected to switch arm 5i of double throw switch D andits switch contact 58 is electrically connected to the switch arm of thedouble throw switch E. The switch contacts 59 and 58 of double throwswitch A' are in turn respectively connected to the switch arms 51 ofdouble throw switches B' and C'.

Current for the operation of constant speed motor 5t is provided to oneterminal of the motor through a conductor 55, a fixed resistance 6i, avariable resistance 52, and conductor 63 connected to terminal 5d of theterminal board 53, terminal i3d in turn being connected to a source ofcurrent through conductor 55. The other terminal of motor 55 is groundedthrough a conductor 55. A filter condenser 51 is preferably provided tominimize radio interference in the operaticn of the motor. Current forthe energization of relays 35 is also provided from the same source ofcurrent through conductor 55, terminal 64, conductor 53, and conductor68, the latter conductor connecting the switch arm of double throwswitch A to conductor 53. The housing for the timer (not shown) isinternally grounded through a conductor 59 connected to terminal it.This arrangement of electrically connected double throw switches betweenthe terminals i5- 52 and the common source may be termed `a Tanning-outcircuit arrangement.

The operation of my apparatus to successively supply current toterminals 45-52 of the terminal board, and thereby successively to therelays 35, depends upon the relative circumferential positioning cf camsA-G on the cam. shaft 55. With the cams positioned as shown in Figs. land 2, current is being supplied to terminal 52 and therefore to therightmost relay 35 (as seen in Fig. i) of propeller I3, through doublethrow switches A', C', and G'. Upon further revolution of the cam shaft,in a clockwise direction as seen in Fig. l (remembering that all camsare xedly, and therefore non-rotatably, mounted on the cam shaft), thedouble throw switch that will be first operated is A'. When this occursthe supply of current to terminal 52 of the terminal board will be cutoff and current will be supplied to terminal d5 through double throwswitches A', B' and D'. The supplying of current to terminal i5 willcontinue until the cam shaft has rotated through approximately 45degrees, at which time the switch arm of double throw switch D will bepermitted by cam D to move from its contact with its switch contact 59into contact with its switch contact 58. Thus, terminal 55 will besupplied with current through double throw switches A', B', and D. Upona further revolution of the cam shaft through approximately 45 degreesthe switch arm 51 of double throw switch B' will be permitted by cam Bto move from contact with its switch contact SQ into contact with itsswitch contact 53. By this means, terminal 41 will be supplied withcurrent through double throw switches A', B' and E'. Further rotation ofthe cam shaft will successively cause the supply of current to terminal48 through double throw switches A', B and E', to terminals d@ and 5i),successively, through double throw switches A', C' and F', and toterminals 5| and 52, successively, through double throw switches A', Cand G. Thus, in one revolution of the cam shaft each of the terminals45-52 is successively and individually supplied with current, eachdouble throw switch being operated twice during the revolution and eachof the terminals being supplied for the same portion of the revolution.

The length of time any one pair of heating elements, or any one heatingcircuit, is supplied with current is thus dependent upon the speed withwhich motor 54 drives the cam shaft 55. The speed of the motor may bevaried by adjustment of the variable resistance B2. In most cases thisadjustment is made during installation of the de-icing equipment anddepends upon the type of propeller blades and heaters. In other casestwo or more taps (not shown) may be taken off resistor B2 and runthrough suitable terminals and connections to the pilots compartment ofthe airplane to make it possible for the pilot to select different camshaft speeds depending upon icing conditions, outside temperature, etc.as will be readily understood by anyone familiar with the art. Thecontrol switch for turning on and ofi of the complete de-icing systemmay of course also be located in the pilot's compartment.

A modified form of apparatus according to my invention is illustrated inFig. 3 as applied to four 3-bladed propellers. As previously pointedout, in the case of 3-bladed propellers the heating elements in all ofthe blades of one propeller must be energized at the same time if acondition of unbalance is to be avoided. Therefore, each of 3-bladedpropellers I0', H', I2' and I3' is provided with but one heatingcircuit, all of the heating elements of the particular propeller beingconnected in the one heating circuit. One terminal of each is againconnected to a slip ring I8 which is grounded through a brush 20'. Theother terminal of the circuit is connected to a slip ring 22 throughwhich current may be supplied to it from brush 23', conductor 21', andrelay armature 3 I from a common source of current for the heatingcircuits of all of the propellers, when the armature is in contact withrelay contact 29'. It will be clear that but one relay 3Q' need beprovided for each propeller and that therefore only four circuits mustbe successively supplied with current by my modied apparatus. As was thecase with respect to the control of the heating elements of Fig. 1, eachof the relays 3U has one terminal grounded at 34 and the other connectedto a terminal on a terminal board 53' by a suitable conductor. The fourterminals on the terminal board 53 to which the relays are connected byconductors 35', 31', 38', and 39' may be designated, respectively, 45',4B', 41 and 48'.

My apparatus for successively supplying current to each of terminalsi5-138' again comprises a constant speed electric motor 54 supplied withcurrent at one terminal through conductor 50', fixed resistance 6I',variable resistance 52', conductor E3', terminal 64 on the terminalboard 53', and a conductor 65' connecting this terminal to a source ofcurrent. The other terminal of the motor is grounded through conductor66 and the housing (not shown) internally grounded through conductor69'. In this modified form, only three cams H, J, and K are required.These cams are all iixedly mounted on a single cam shaft driven by motor54' and serve to operate double throw switches H', J and K.

As indicated in Fig. 3, my apparatus is in position to supply current toterminal 48' through double throw switches I-I and K', the switch armcam; shaft has rotated another 90. degrees.

:to operate all ofthe double throwswitches.

of double throwV switch H' 'being electrically :con-

:nected to'conductor. .63. by conductor 68. .Upon

revolution of the` cam shaft .in a clockwise direction, as indicated,the switch arm `of double throw switch H' will be moved upwardlybreakingthe. circuit to terminal 48' and completing one to terminal d' throughdouble throw .switch J As the cam shaft continues to rotate,.and..afterit has rotated approximately 90 degreesin this form of apparatus, theswitch arm of double throw .switch J will be permitted to fall, wherebyvthe supply of current toY terminal d5 will .be discontinued'anda supplyof current to fli.;initiated. The. next switch to be operated lupon thefurther vrevolution of the cam shaft will .be H,;the;switch arm of whichwill be permitted toV fall .afterV the r:This will discontinue thesupply of .current to terminal 46' .and initiate the supply of currentto terminal 41. because, by this time, the switch arm of double .throwswitch K will have been moved upwardly,

as viewed in the drawing, by cam K.

Another modilied forni of apparatus according Y.to my inventionisillustrated in Fig. 4 and is comparable to that illustrated in Fig. 3 inthat itis adapted to be used for the energization of the heatingelements in four B-bladed propellers through terminals 45" to d8" andconductors 36" to 39". Additionally, it comprises, -asdoes the formillustrated in Fig. 3, a constant speed electric motor 54" supplied withcurrent at one terminal through conductor G", nxed resistance. 6 l vari-.able resistance 62", conductor c3", terminalt" on the terminalboardtll", and a conductor 55" connecting this terminal to a source of.current.

The other terminal of the motor is grounded through conductor E6" andthe housing (not shown) internally grounded through conductor 69"..Three double throwswitches L, M, and N, respectively, .are electricallyconnected to one another in a tanning-out circuit arrangement betweenconductor 68, .which is continuously supplied with current from thecommonsource, and terminals 45 to d8 in the same .way aswere doublethrow switchesH', J and K intheimodi .cation of Fig. 3.

scribed forms of my invention,y but they are so arranged in this formthat in each .theV switch `arm is normally urged toward the. cam. AThisresults in double throw switchi N being` in an inverted position ascompared .tothe Yposition of the comparable double throw switch K in 3.However, to .maintain for descr-iptivepurposes the sequential'supplyingof current to terminals-d to 48 respectively the electrical conductorsfrom .the switch contacts of double throw switch N are criss-crossed. Aswill be noted from Fig. 4, cam P has a dwell or approximately 1.30degrees.

As indicated in Fig. 4 the apparatus isfinaposition to supply current toterminal 35' through double throw switches L and M, the switch-arm ofdouble throw switch L being electrically connected to conductor 83" byconductor S8". 'Upon revolution of cam shaft", and therefore cani P,through about 90 degrees in a clockwise direction, as indicated, theswitch arm of "double throw switch M will be permitted Ato/move down--wardlybreaking the circuit Yto terminal y45" and completing one toterminal 46". During this rotation of the cam shaft and cam the switcharm of double lthrow switch'N will` be moved downwardly in preparationforthe supplying of current to terminal` 4'1". As the cam shaftcontinues to rotate and after it has rotated through another degrees theswitch arm of double throw switch L will be moved to the left, as seenin the drawing, and current will be supplied to terminal lll" throughswitch L and .switch N. After another 90 degrees of rotation of the camshaft and cam the switch arm of double throw switch N will be permittedto move upwardly whereby current is then supplied to terminal 43 throughswitches L and N. During this last 90 degrees of rotation of the camshaft'and cam the switch arm of double throw switch M will be movedupwardly to prepare the circuit for the supply of current to terminal45". This last-mentioned circuit will be completed when the cam shaftand cam have been rotated through yet another 90 degrees to theirposition as shown in the drawing at which time the switch arm of doublethrow switch L is permitted to move to the right as seen in the drawing.This completes one cycle of operation of the vapparatus.

In all forms of my apparatus it will be noted that the primary doublethrow switches (A, H and L) perform two electrical transfers in onecycle while the secondary double throw switches (B', C', D', E', F', G',J', K', M and N) perform one electrical transfer during a completecycle.

In the interest of simpliiication, I have shown, for instance in Fig. 1,all switches as having simple movable arms 57 operated by cam followers56. However, in order to avoid any appreciable interval between thebreaking of one circuit, when an arm 5l leaves a contact and the makingof the succeeding circuit, when the arm touches the correspondingcontact 59, caused by the gradual rise of follower 5t on the cam asshaft 55 slowly rotates,.I prefer to use any of the several commerciallyavailable single pole double thrown lsnap action switches, whereby, thecircuit transfer occurs rapidly and independently of the rate of motionof the cam shaft 55. Thus, the utilization of current from the commonsource is almost continuous, providing uniform loading of `thegeneratorand most eiiicient use of the generating equipment.

As was the case with the apparatus used for successively supplyingcurrent to eight circuits, the ones shown in Fig. 3 and 4 for supplyingcurrent to but four circuits will require the operation of each doublethrow switch twice per cycle or revolution of the cam shaft. Thus, in noform of my invention must any switch be operated more than twice in onecomplete cycle. This provides a very definite advantage over theapparatus disclosed in the Hoof Patent 2,466,238, wherein a double throwswitch is operated eight times for eight circuit operation and fourtimes for four circuit operation. The switch life in an apparatusdesigned to control eight circuits is thus increased by 300%, or fourtimes, while that of apparatus designed to control four circuits isincreased by or doubled. Comparable increases in switch life forapparatus designed, according to my invention, to control diiierentnumbers of circuitsV may be achieved. For instance, in a six circuitapparatus switch life will be increased by 209% or three times.

Among the advantages of my apparatus are its simplicity, its consequentlow cost, and its longer life in use before requirement for replacementof any of its parts. It will, of course, be understood that variousminor changes and modifications may be made in the apparatus withoutdeparting from the invention as set forth in the appended claims.

I claim:

1. Apparatus for successively supplying current from a common source toa plurality of electric circuits which comprises a plurality of doublethrow switches electrically connected in a fanning-out circuitarrangement between the common source and the plurality of electriccircuits; a constant speed electric motor; and means mechanicallyconnecting the motor to the double throw switches to cause the doublethrow switches to be operated in seouence when the motor is operated,said mechanical connecting means being so constructed and arranged thateach double throw switch performs at least one electrical transferduring a complete cycle of o-peration of the apparatus and each electriccircuit is successively supplied with current from the common source4during the cycle of operation.

2. Apparatus for successively supplying current from a common source toa plurality of electric circuits which comprises a primary double throwswitch electrically connected to the common source; a plurality ofsecondary double throw 'switches electrically connected in a tanning-outcircuit arrangement Ibetween the primary double throw switch and theplurality of electric circuits; a constant speed electric motor; andmeans rnechanically connecting the motor to all of the double throwswitches, said mechanical connect ing means being so constructed andarranged that each of the double throw switches is operated twice duringa complete cycle of operation of the apparatus, the primary double throwswitch performs two electrical transfers during the complete cycle ofoperation of the apparatus and the secondary double throw switchesperform one electrical transfer each during the complete cycle ofoperation, each electric circuit thereby being successively suppliedwith current from the common source during the cycle of operation.

3. Apparatus for successively supplying current from a common source toa lplurality of electric circuits which comprises iirst and seconddouble throw switches the switch contacts of which are electricallyconnected respectively to the terminals of the electric circuits, eachdouble throw switch controlling two circuits, a third double throwswitch, the switch contacts of which are electrically connected to theswitch arms of the first and second Adouble throw switches and theswitch arm of which is adapted to be electrically connected to thecommon source; a constant speed electric motor; a cam shaft driven bysaid motor; a plurality of substantially identical cams fixedly andnon-rotatably mounted on the cam shaft, each of the cams being adaptedto operate one of the double throw switches, the cams beingcircumferentially positioned relative to one another so that during thefirst half of one revolution of the cam shaft the iirst double throwswitch is operated, the third double throw switch being positioned tosupply current to said iirst double throw switch, and during the secondhalf of the revolution of the cam shaft the second double throw switchis operated, the third double throw switch being now positioned tosupply current to the second double throw switch, whereby during onerevolution of the cam shaft each electric 10 circuit will besuccessively supplied with current from the common source.

4. Apparatus for successively supplying current from a common source toa plurality of electric circuits which comprises rst and second doublethrow switches each having two switch contacts and a switch arm adaptedto be moved into engagement with either of its switch contacts, raidswitch contacts each being electrically connected to one terminal of oneof said electric circuits; a third double throw switch having a switcharm adapted to be electrically connected to said common source andhaving two switch contacts one of which is electrically connected to theswitch arm of said first double throw switch and the other of which iselectrically connected to the switch arm of said second double throwswitch; a constant speed electric motor; a cam shaft driven by saidmotor; a cam for each double throw switch fiXedly mounted on said camshaft, said cams being operable to move the switch arms of theirrespective dou-ble throw switches into contact with the switch contactsof the respective double throw switches, each cam being substantiallyidentical to the other cams and being shaped to move its respectiveswitch arm into engagement with one switch contact during approximatelydegrees of its revolution and into engagement with the other switchcontact during the remaining approximately 180 degrees, said cams beingcircumferentially positioned on the cam shaft relative to one another sothat during approximately the first half of one revolution of the camshaft the switch arm of said third double throw switch will be incontact with that one of its switch contacts which is electricallyconnected to the switch arm of said first double throw switch and duringthe second half of the revolution will be in contact with that one ofits switch contactsl electrically connected to the switch arm of saidsecond double throw switch and so that during said first half of therevolution of the cam shaft the switch arm of the first double throwswitch will be in contact first with one of its switch contacts and thenwith the other of its switch contacts and during the second half of therevolution of the cam shaft the switch arm of said second double throwswitch will be in contact first with one of its switch contacts and thenwith the other of its switch contacts, whereby during one revolution ofthe cam shaft each electric circuit will be successively supplied withcurrent from the common source.

5r. Apparatus for successively supplying current from a common source toa plurality of electric circuits which comprises first and second doublethrow switches the switch contacts of which are electrically connectedrespectively to the terminals of the electric circuits, each doublethrow switch controlling two circuits, a third double throw switch, theswitch contacts of which are electrically connected to the switch armsof the first and second double throw switches and the switch arm ofwhich is adapted to be electrically connected to the common source; aconstant speed electric motor; a cam shaft driven by said motor; a camhaving a dwell of approximately 180 degrees fixedly mounted on said camshaft and adapted to operate each double throw switch twice during acomplete cycle of operation of the apparatus, the three double throwswitches being so positioned and arranged about said cam that the thirddouble throw switch performs two electrical transfers during thecomplete cycle of op- 1 (algemener u 1 I f 1 2l eration andeach of therst 'and the second double'` v r Y throw switches performsoneelectricalttransfer- REFERENCES CITED during the cycle ofoperation;eachl electric circuit thereby beingsuccessively supplied.with. current r le: 0f thlsvpatenff from the common source during the.cyclezfofi: 5 UNITED STATESfpAfI'ENTS operation. e e e o HUH Number NameDate ART W' HAYDON' 2,466,238 Hoof Apr. 5, 1949 The) following-references'are of record in thel

